Road finishers are provided with a large number of heating elements and heating units which heat a great a great variety of work components that come into contact with the heated paving material for producing road surfaces, so as to avoid, on the one hand, premature cooling of said paving material and so to prevent, on the other hand, the paving material from solidifying on and adhering to the cold surfaces of the respective work component. These heating units must be supervised so as to guarantee in any case that the predetermined temperature of the work component is reached and maintained. U.S. Pat. No. 6,334,735, for example, discloses an automatically controlled heating system for a road finisher in which a control system is used, which automatically adjusts the flow of current through the heating element so as to regulate the temperature. For supervising the heating unit and the temperature produced by said heating unit, at least one temperature sensor is used. A temperature sensor, especially when used in the manner described, is, however, unable to satisfactorily supervise each individual heating unit, especially each individual heating rod in a heating unit, so as to find out whether the heating rod in question is faulty or whether it works correctly. It can only be detected whether the heating unit in its entirety is able to reach and maintain the desired temperature.
A faulty heating unit could, however, be repaired much more easily, if it were possible to find out immediately that one of the heating rods is faulty and which one it is.